1. Field of the Invention
The present invention relates to a tandem color electrophotographic machine, and, more particularly, to margin alignment and plane-to-plane registration in a tandem color electrophotographic machine.
2. Description of the Related Art
Tandem color printing enables color electrophotographic printing to be performed by a printer at the same speed as black-and-white (mono color) electrophotographic printing. Such a tandem process utilizes four separate imaging devices to simultaneously create four separate latent images on four different photoconductive surfaces. Thus, all four colors can be imaged, developed, and transferred to the desired media at the same speed as a single color could be printed. Single color printers all implement techniques to align the top of the page, left margin, line length, and page length. In a tandem configuration, an additional difficult problem arises in registering each color image plane accurately relative to all the other color image planes. Manufacturers have been hesitant to produce tandem color laser printers because of the difficulty in maintaining alignment and plane-to-plane registration due to manufacturing tolerances.
What is needed in the art is a method of aligning the registration of all color planes in both the process direction (media direction of travel) and the scan direction (cross process direction).
The present invention provides a method of setting the margins and plane-to-plane registration at factory calibration and in field adjustments. The present invention utilizes print element (PEL) slice insertion, mirror motor synchronization, and additional techniques to achieve the desired initial registration.
The invention comprises, in one form thereof, a method of setting a plurality of margins in an electrophotographic machine. A top margin for a reference color black is set by establishing a first time delay between a vertical synchronization signal and a first line. A right margin or a left margin for the reference color black is set by establishing a second time delay between a horizontal synchronization signal and a start of printing. The other of the right margin and the left margin is set by adjusting a scan speed of a laser beam across a photoconductive element and adjusting a process speed in the cross-scan direction including speed of the photoconductive element, image accumulation member, and print medium. A bottom margin for the reference color black is set by adjusting the process speed. The other three colors, cyan, magenta, and yellow, are then registered to the reference color black.
An advantage of the present invention is that margins and plane-to-plane registration can be set at factory calibration and in field adjustments in order to compensate for manufacturing tolerances.